The present invention relates to a structure for supporting a rotating shaft of a turbocharger, and particularly to a bearing structure having rolling contact bearings.
In one conventional example of a bearing structure for a turbocharger of an engine, each rolling bearing is preloaded in a thrust direction by a preloading spring whose spring constant is chosen as being great enough to receive maximum thrust of a rotating shaft of the turbocharger. In this structure, however, a preload applied on each rolling bearing is constant, and therefore it becomes excessive in a low engine speed range. As a result, frictional resistance of each rolling bearing is increased, and performance of the turbocharger especially in the low engine speed range is deteriorated.